Two Fine Gael senators have become the latest to rebel over contentious abortion legislation.

As the divisive Bill passes through the Seanad with the first round of votes taking place later, Fidelma Healy Eames and Paul Bradford voted against the Government.

Ms Healy Eames confirmed earlier that she could not support the Protection of Life During Pregnancy Bill 2013 as it stands, claiming it is unconstitutional.

"I don't want to lose the Fine Gael party whip but I do want to exercise my human right to make a conscientious decision," Ms Healy Eames said.

"Almost every Western democracy provides for a free vote on issues like abortion. Why don't we have the confidence to trust our parliamentarians to make the right decision?"

Five Fine Gael TDs, including former junior minister Lucinda Creighton, have already lost the party whip after their backbench revolt during two night sessions in the Dail last week.

Mr Bradford, who is married to Ms Creighton, claimed that abortion goes against the fabric of Fine Gael's election promise.

The landmark laws enshrine a woman's right to a termination if her life is at risk, including from suicide. They passed through the Dail last week with a comfortable majority of 127 votes to 31.

The upper house began debating it on Monday and will continue through Tuesday, Wednesday and Thursday. The final stages of the legislation are scheduled for Monday and Tuesday next week, when the final vote to pass it will be held.

Once passed through Seanad, and provided there are no demands for further amendments, the legislation will be brought to President Michael D Higgins who will sign off on it and enshrine it into Irish law.